Lepidocrocite potassium magnesium titanate, method for manufacturing the same and friction material

ABSTRACT

Lepidocrocite potassium magnesium titanate having a composition represented by the formula K 0.2-0.7 Mg 0.4 Ti 1.6 O 3.7-4  and obtainable by subjecting an aqueous slurry of lepidocrocite potassium magnesium titanate having a composition represented by the formula K 0.8 Mg 0.4 Ti 1.6 O 4  to an acid treatment and subsequent calcination.

TECHNICAL FIELD

This invention relates to lepidocrocite potassium magnesium titanate, amethod for manufacturing the same and a friction material.

BACKGROUND ART

Friction materials as heretofore used to form braking members utilizeasbestos in the form of being dispersed in and integrated by organic orinorganic binders. However, these show insufficient heat resistance andfrictional wear properties, e.g., friction coefficient and wearresistance, that tend to drop in the high-temperature range, resultingin the increased occurrence of a fading phenomenon when braking iseffected. When braking is effected, the contact of such frictionmaterials with a high-speed brake disc causes the frequent occurrence of“braking noise”. Also, asbestos is a known cancer-causing substance andis readily made into dusts. In view of the environmental hygienicproblem that workers may inhale asbestos during operation, the use ofasbestos has been increasingly self-restrained. Under thesecircumstances, it has been strongly demanded to develop asbestossubstitutes.

In response to such demands, friction materials using non-carcinogenicpotassium titanate fibers as a friction control agent have been proposedand achieved a widespread use for incorporation primarily in automobilebraking pads. The friction materials containing potassium titanatefibers exhibit superior sliding properties and good braking effect.Nevertheless, they provide little damage to braking discs, which is avery favored advantage thereof. However, they suffer from insufficientwear resistance, particularly in the high-temperature range, and aslightly faster wear rate. Also, they have not yet offered a sufficientsolution to “braking noise” developed in braking devices. Further, thepotassium titanate fibers, because of their fibrous form, are bulky andpoor in flowability, leading to their tendency to deposit on a wall of afeed passage and block the passage during manufacture of frictionmaterials, which has been a problem.

Japanese Patent Laying-Open No. Hei 5-221759 describes potassiummagnesium titanate having an orthorhombic layer structure, i.e.,lepidocrocite potassium magnesium titanate, with a compositionrepresented by the formula K_(0.8)Mg_(0.4)Ti_(1.6)O₄, a major diameter(length) of 5 mm, a minor diameter (breadth) of 2-3 mm and a thicknessof 0.1-0.5 mm. Also, Japanese Patent Registration No. 3027577 describesthe utility of lepidocrocite potassium magnesium titanate as a frictioncontrol agent for friction materials. Such friction materials exhibitstable frictional wear properties in the low-to high-temperature ranges.However, since a contact temperature between the brake disc and brakepad is high and reaches 1,000° C. or over, their heat resistancesometimes becomes insufficient for the long-term continuous use, e.g.,for over several tens hours, possibly resulting in the reduced wearresistance in the high-temperature range and the increased wear amount.There accordingly remains a need for development of friction materialswith further improved heat resistance and frictional wear properties.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide novel lepidocrocitepotassium magnesium titanate that, when used as a friction controlagent, further improves heat resistance and frictional wear properties,a method for manufacturing the same and a friction material using thesame.

After energetic and continued studies in the attempt to accomplish theabove-described object, the inventors of the present invention havecompleted the present invention by successfully obtaining novellepidocrocite potassium magnesium titanate suitable for use as afriction control agent, as well as friction materials which showremarkably improved heat resistance and frictional wear properties andalso enjoy satisfactory productivity.

That is, this invention is concerned with lepidocrocite potassiummagnesium titanate with a composition represented by the formulaK_(0.2-0.7)Mg_(0.4)Ti_(1.6)O_(3.7-4), method for manufacturing the sameand friction materials using the same.

The manufacturing method of the present invention is characterized asincluding the steps of adding an acid to an aqueous slurry oflepidocrocite potassium magnesium titanate having a compositionrepresented by the formula K_(0.8)Mg_(0.4)Ti_(1.6)O₄ while adjusting theslurry to a pH of 6-9, preferably 6.5-8.5, more preferably 6.5-7.5,separating solids from the slurry and then calcining the solids.

The friction control agent of the present invention is characterized ascomprising lepidocrocite potassium magnesium titanate either of thepresent invention or made by the practice of the manufacturing method ofthe present invention.

The friction material of the present invention is characterized ascontaining 1-80% by weight of lepidocrocite potassium magnesium titanateeither of the present invention or made by the practice of themanufacturing method of the present invention.

Lepidocrocite potassium magnesium titanate of the present invention(hereinafter abbreviated as “KTMO” unless otherwise particularlyspecified) has a layer structure and shows stable heat resistance andfrictional wear properties regardless of temperature. Also, since itdoes not exist in a fibrous form, unlike potassium titanate fibers, itis very unlikely to block a feed passage during manufacture and worsen aworking environment due to the presence of respirable fibers.

Friction materials containing KTMO as a friction control agent are ableto exhibit extremely stable heat resistance and frictional wearproperties (such as friction resistance and frictional coefficients)over the low to high-temperature ranges. Their heat resistance andfrictional wear properties are maintained extremely stable even during along-term use over several tens hours.

Accordingly, the use of the friction material of this invention forbraking members, e.g., clutch facings, brake linings and disc padsincorporated in braking devices as of automobiles, aircrafts, railwayvehicles and industrial apparatuses not only improves and stabilizestheir braking functions but also extends their service lives.

The reason why the friction materials containing KTMO of the presentinvention provide such superior results is not clear but presumablyattributed to a higher melting point of KTMO of the present inventionrelative to prior art lepidocrocite potassium magnesium titanaterepresented by the composition K_(0.8)Mg_(0.4)Ti_(1.6)O₄ and also to thestructural difference therebetween.

The lepidocrocite potassium magnesium titanate (KTMO) of the presentinvention generally has a composition represented by the formula:K_(0.2-0.7)Mg_(0.4)Ti_(1.6)O_(3.7-4)  (1)and has an orthorhombic layer structure. In view of frictional wearproperties, the preferred KTMO is represented by the formulaK_(0.2-0.5)Mg_(0.4)Ti_(1.6)O_(3.7-4)  (2)and has a potassium content within the range of 0.2-0.5 moles. KTMO ofthe present invention generally has a flaky or sheetlike shape assimilar to mica, pulverized pieces of shells and the like.

The virtual correspondence of the X-ray diffraction chart (FIG. 1) forKTMO of the present invention to the X-ray diffraction chart (ICDD cardNo. 35-0046, FIG. 2) for the prior art lepidocrocite potassium magnesiumtitanate (hereinafter referred to as “KTMO-a”) represented by theformula:K_(0.8)Mg_(0.4)Ti_(1.6)O₄  (a)suggests that KTMO of the present invention is probably maintained in acrystal condition that lacks a part of potassium but retains theorthorhombic layer structure.

As potassium is generally eliminated in the form of K₂O, the compositionof the lepidocrocite potassium magnesium titanate of the presentinvention is considered to be represented by the formula:K_(x)Mg_(0.4)Ti_(1.6)O₄-ywhere x satisfies x=0.2−0.7 and y satisfies y=(0.8−x)/2.

However, it is difficult to measure accurately the oxygen compositionratio in the actually manufactured compound. Therefore, in thistechnical field, assuming that oxygen is not eliminated, the compoundmay be represented by the formula:K_(x)Mg_(0.4)Ti_(1.6)O₄which should be regarded as the same compound represented by the aboveformula.

Also, thermal analysis (TG DTA, FIG. 3: KTMO of the present invention,FIG. 4: KTMO-a) revealed a melting point of about 1,375° C. for thesubstance KTMO of the present invention and a melting point of about1,300° C. for the known substance KTMO-a. In this regard, they areevidently dissimilar inorganic substances.

An arithmetic mean of major and minor diameters ((major diameter+minordiameter)/2), a proportion of a major to minor diameter (majordiameter/minor diameter) and a mean thickness for KTMO of the presentinvention spread over a wide range of values and may be suitably chosendepending upon the end use contemplated. In order to impart satisfactoryheat resistance and sliding properties to friction materials containingKTMO as friction control agent, KTMO may be used having an arithmeticmean of major and minor diameters generally in the approximate range of0.1-100 μm, preferably in the approximate range of 1-30 μm, a proportionof a major to minor diameter of from 1 to below 5, preferably from 1 tobelow 3, and a thickness generally in the range of 50-5,000 nm,preferably in the range of 200-2,000 nm These values for major and minordiameters and thickness are determined by a scanning electronmicroscope. The arithmetic mean of major and minor diameters, proportionof a major to minor diameter and mean thickness are arithmetic averagesof values determined for about 20 particles, respectively. The majordiameter is the longest diameter of each flake particle in its sheetlikeflat plane. The minor diameter is the shortest diameter of each flakeparticle in its sheetlike flat plane.

The particularly preferred KTMO has an arithmetic mean of major andminor diameters generally in the approximate range of 0.1-100 μm, aproportion of a major to minor diameter of from 1 to below 5 and athickness generally in the range of 50-5,000 nm, and exists in the formof flakes.

KTMO of the present invention can be manufactured, for example, byadding an acid to an aqueous slurry of KTMO-a, mixing them, separatingsolids from the slurry and calcining the solids.

KTMO-a can be obtained, for example, by mixing sources of titanium,potassium and magnesium, adding a flux and, subsequnet to thoroughmixing, calcining the mixture at a temperature of 1,000-1,100° C. for aperiod of 1-8 hours.

The titanium source can be optionally chosen from titanium-containingcompounds, specific examples of which include titanium oxide, rutileore, titanium hydroxide wet cake, water-containing titania and the like.Such titanium sources may be used alone or in combination.

The potassium source can be chosen from compounds which producepotassium oxide when exposed to heat, specific examples of which includepotassium oxide, potassium carbonate, potassium hydroxide, potassiumnitrate and the like. Such potassium sources may be used alone or in anycombination. Also, the potassium source may be used in combination witha small amount of one or more of oxides, carbonates, hydroxides andnitrates of any other alkaline metal.

Examples of magnesium sources include magnesium hydroxide, magnesiumcarbonate, magnesium fluoride and the like. Such magnesium sources maybe used alone or in any combination.

The titanium, potassium and magnesium sources are mixed in the standardratio of Ti:K:Mg=4:2:1 (molar ratio), with each being permitted todeviate within about 5%. However, a large deviation from the specifiedratio sometimes results in the unfavorable deposition of a side product,K₂MgTi₇O₁₆, which is not sheetlike.

Examples of fluxes include potassium chloride, potassium fluoride,potassium molybdenate, potassium tangstenate and the like. Among thosefluxes, potassium chloride is particularly preferred. The flux is addedto the raw material in the molar ratio (raw material:flux) of 3:1-3:15,preferably 3:3-3:10. Lower loadings of the flux increase an economicaladvantage. However, if the flux loading is excessive, the unfavorablecollapse of a sheetlike crystal may result.

Calcination can be achieved using an optional technique such as anelectric furnace, muffle furnace or the like. In the mass production, atunnel kiln may preferably be used to calcine the raw materialpreviously pressed into a bricklike or cylindrical shape. Preferably,calcination is performed at a temperature between 1,000-1,100° C. for aretention period of 1-24 hours. Temperature may be raised or lowered atany rate, but generally preferably at 3-7° C./min. The highercalcination temperatures result in larger-scale sheetlike products.However, if it exceeds 1,100° C., the product shape may be impaired dueto fusion, which is an unfavorable result. The longer retention periodincreases the size of resulting particles. After calcination, theproduct may be wet disintegrated. Specifically, it may be crushed andground using a jaw crusher, a bin mill and the like, dispersed in waterand stirred in the form of a 5-10 wt. % slurry. When needed, this slurrymay be further subjected to a sequence of classifying filtering anddrying to obtain a sheetlike potassium magnesium titanate (KTMO-a).

The concentration of the aqueous slurry of KTMO-a is not particularlyspecified and may be suitably chosen from a wide range. In view ofworkability, the aqueous slurry may be maintained at a concentration ofabout 1-30 weight %, preferably about 2-15 weight %.

The acid used is not particularly specified in type and can be chosenfrom known acids, examples of which include inorganic acids such assulfuric acid, hydrochloric acid and nitric acid; organic acids such asacetic acid; and the like. Such acids may be used in combination, whenneeded. The acid may be added to the aqueous slurry in the effectiveamount to maintain the aqueous slurry at a pH of 6-9, preferably at a pHof 6.5-8.5, more preferably at a pH of 6.5-7.5. The pH measurement ofthe aqueous slurry is performed after addition of the acid and followingabout 1-5 hours of stirring. The acid is generally used in the form ofan aqueous solution. The concentration of the aqueous acid solution isnot particularly specified and may be suitably chosen from a wide range.It may be generally maintained in the approximate range of 1-80 weight%.

After the pH of the aqueous slurry is adjusted to fall within theabove-specified range, the solids present therein is separated by aconventional separating means such as filtering, centrifuging or thelike. The separated solids may be washed with water, if necessary.

The solids is then calcined. Generally, calcination is carried out at atemperature of about 400-700° C. and completes after about 1-12 hours.After calcination, the resulting powder may be pulverized or passedthrough a screen for disintegration.

The above-described procedure results in obtaining KTMO of the presentinvention.

The present invention also provides a friction material containing KTMOas a friction control agent. The friction material of the presentinvention contains a binder and a friction control agent as essentialcomponents.

Any binder which is conventionally used in the friction material fieldcan be used. Examples of binders include organic binders and inorganicbinders. Examples of organic binders include thermosetting resins suchas a phenol resin, formaldehyde resin, melamine resin, epoxy resin,acrylic resin, aromatic polyester resin and urea resin; elastomers suchas a natural rubber, nitrile rubber, butadiene rubber, styrene butadienerubber, chloroprene rubber, polyisoprene rubber, acrylic rubber, highstyrene rubber and styrene propylene diene copolymer; thermoplasticresins such as a polyamide resin, polyphenylene sulfide resin, polyetherresin, polyimide resin, polyether ether ketone resin and thermoplasticliquid crystal polyester resin; and the like. Examples of inorganicbinders include an alumina sol, silica sol, silicone resins and thelike. The above-listed binders may be used alone or in any combination,if compatible.

Used for a friction control agent is KTMO of the present invention asrepresented by the above-specified formula (1).

The friction material of the present invention may further contain afibrous substance. Any fibrous substance which has been conventionallyused in the art is applicable. Examples of fibrous substances includeresin fibers such as aramid fiber, metal fibers such as steel and brassfibers, carbon fibers, glass fibers, ceramic fibers, rock wool, woodpulp and the like. These fibrous substances may be used alone or incombination. Also, these fibrous substances may be subjected to asurface treatment using a silane coupling agent such as an aminosilane,epoxysilane or vinylsilane coupling agent, a titanate coupling agent,phosphate ester or the like, for purposes as of improving theirdispersion properties and adhesion to binders.

The friction material of the present invention may also contain afriction control agent conventionally used in the art, within the rangethat does not impair the favored properties of the friction material,examples of which include organic powders such as natural or syntheticrubber powders, either vulcanized or unvulcanized, cashew resin powders,resin dusts and rubber dusts; inorganic powders such as carbon black,graphite powder, molybdenum disulfide, barium sulfate, calciumcarbonate, clay, mica, talc, diatomite, antigorite, sepiolite,montmorillonite, zeolite, sodium trititanate, sodium hexatitanate,potassium hexatitanate and potassium octatitanate; metal powders such ascopper, aluminum, zinc and iron; oxide powders such as alumina, silica,chromium oxide, titanium oxide and iron oxide; and the like. Theseconventional friction control agents may be used alone or in anycombination thereof.

The friction material of the present invention may further contain oneor more of a rust-preventive agent, lubricant and abrasive.

The components of the friction material of the present invention can beblended in the proportions that can be suitably chosen from a wide rangedepending upon various conditions including the types of the binder,optional fibrous substance, conventional friction control agent andother additives used, the sliding and mechanical properties sought forthe resulting friction materials, the end uses contemplated and thelike. Generally, the friction material may contain 5-60 weight %(preferably 10-40 weight %) of a binder, 1-80 weight % (preferably 3-50weight %) of a friction control agent (inclusive of a conventionalfriction control agent), up to 60 weight % (preferably 1-40 weight %) ofa fibrous substance and up to 60 weight % (preferably 5-50 weight %) ofother additives, based on the total amount of the friction material.

The preferred friction material contains the fibrous substance, togetherwith the binder and friction control agent, as essential components.

The friction material of the present invention can be manufactured byvarious techniques known in the art as being useful for manufacture offriction materials. To illustrate one technique, a fibrous substance, ifneeded, is dispersed in a binder, a friction control agent and otheroptional components are subsequently added to the binder, either as amixture or separately, and the resulting mixture is brought into a moldwhere it is integrated by application of heat and pressure.

Alternatively, a technique may be used whereby the binder is meltkneaded in a twin screw extruder into which the friction control agent,optional fibrous substance and other components, either as a mixture orseparately, are fed through a hopper and the resulting extrudate ismachined into a desired shape.

Also alternatively, a technique can be used whereby the fibroussubstance, if necessary, is dispersed in the binder to which thefriction control agent and other optional components are subsequentlyadded to form a mixture, the mixture is dispersed such as in water andwet laid on a net and then dewatered into a sheet, the sheet is pressedand heated for integration by a press machine, and the resulting productis properly cut and polished into a desired shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray diffraction chart of lepidocrocite potassiummagnesium titanate of the present invention;

FIG. 2 is an X-ray diffraction chart of lepidocrocite potassiummagnesium titanate previously known in the art;

FIG. 3 is a thermal analysis chart of lepidocrocite potassium magnesiumtitanate of the present invention;

FIG. 4 is a thermal analysis chart of lepidocrocite potassium magnesiumtitanate previously known in the art;

FIG. 5 is a graph showing a relationship between a disc pad temperatureand a wear rate for the disc pads A-F;

FIG. 6 is a graph showing a relationship between a disc pad temperatureand a friction coefficient for the disc pads A-F;

FIG. 7 is a graph showing a relationship between a disc pad temperatureand a wear rate for the disc pads A and F;

FIG. 8 is a photomicrograph (at a magnification of 2,000×) oflepidocrocite potassium magnesium titanate of the present invention whentaken using a scanning electron microscope;

FIG. 9 is a photomicrograph (at a magnification of 2,000×) oflepidocrocite potassium magnesium titanate previously known in the artwhen taken using a scanning electron microscope; and

FIG. 10 is a thermal analysis chart of lepidocrocite potassium magnesiumtitanate of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

The following Examples, Comparative Examples and Test Examplesspecifically illustrate the present invention. In the Examples, “parts”and “%” mean “parts by weight” and “% by weight”, respectively.

EXAMPLE 1

(1) Synthesis of KTMO-a

1473 g of titanium oxide, 638 g of potassium carbonate, 1,003 g ofpotassium chloride, 279 g of magnesium hydroxide and further 200 ml ofwater as a binder were mixed. The mixture was pressed at a pressure of14.7 MPa into a block shape by a hydropressing machine (manufactured byYamamoto Tekkosho, Co., Ltd.). This block was calcined at 1,050° C. for1 hour in an electric furnace (manufactured by Advantech Toyo Co., Ltd.)and then cooled gradually. The calcined product was pulverized to obtaina white powder with an arithmetic mean of major and minor diameters of 3μm, a mean thickness of 300 nm and a proportion of a major to minordiameter of 1.5. The white powder was identified as having a compositionof K_(0.8)Mg_(0.4)Ti_(1.6)O₄ by fluorescent X-ray analysis using an FP(fundamental parameter) method.

FIG. 2 is an X-ray diffraction chart of the white powder obtained. Thediffraction peaks were found to correspond reasonably to those given inICDD card No. 35-0046. FIG. 4 is a thermal analysis chart of the whitepowder obtained and shows TG (thermogravimetric analysis) and DTA(differential thermal analysis) curves. As can be seen from FIG. 4, amelting point was found to be about 1,300° C.

(2) Synthesis of KTMO of the Present Invention

The above-obtained KTMO-a was used to prepare 80 liters of a 2% aqueousslurry to which 526 g of a 76% aqueous solution of sulfuric acid wassubsequently added. The slurry was stirred for 2 hours and then adjustedto a pH of 7.5. This aqueous slurry was subjected to treatment by acentrifugal separator. The resulting cake (solids) was dispensed, driedat 110° C. for 5 hours and then calcined at 600° C. for 12 hours in anelectric furnace. The calcined product was cooled gradually and thenpassed through a 20 mesh screen to obtain a white powder with anarithmetic mean of major and minor diameters of 3 μm, a mean thicknessof 300 μm and a proportion of a major to minor diameter of 1.5. Thewhite powder was identified as having a composition ofK_(0.4)Mg_(0.4)Ti_(1.6)O_(3.8) by fluorescent X-ray analysis using an FP(fundamental parameter) method.

FIG. 1 is an X-ray diffraction chart of the white powder obtained. Thediffraction peaks were found to show resemblance to those of KTMO-ashown in FIG. 2 and correspond reasonably to those given in ICDD cardNo. 35-0046. These suggest that, like KTMO-a, KTMO of the presentinvention most probably has an orthorhombic layer structure.

FIG. 3 is a thermal analysis chart of the white powder obtained. As canbe seen from FIG. 3, a melting point was found to be about 1,375° C.

It is therefore evident that KTMO of the present invention is a compoundclearly distinct from KTMO-a prior to being subjected to an acidtreatment.

A photomicrograph of KTMO when taken using a scanning electronmicroscope is shown in FIG. 8. A photomicrograph of KTMO-a when takenusing a scanning electron microscope is shown in FIG. 9.

EXAMPLE 2

20 parts of KTMO (K_(0.4)Mg_(0.4)Ti_(1.6)O_(3.8)) obtained in Example 1,10 parts of aramid fibers (product name: KEVLAR PULP®, a syntheticaramid, having a mean fiber length of 3 mm), 20 parts of a phenol resin(binder) and 50 parts of barium sulfate were mixed. The mixture waspreformed at a pressure of 29.4 MPa at an ambient temperature for 1minute, integrated in a mold at a pressure of 14.7 MPa at a temperatureof 170° C. for 5 minutes and heat-treated at 180° C. for subsequent 3hours. The molded product was removed from the mold and polished tofabricate a disc pad A (JIS D 4411 test piece).

COMPARATIVE EXAMPLE 1

The procedure of Example 2 was repeated, except that each of thebelow-specified fibrous substances (friction control agents) B-E wasused in the amount of 30 parts instead of using 30 parts of KTMO andaramid fibers, to fabricate disc pads B-E.

Fibrous substance B: potassium hexatitanate fibers (having a sectiondiameter of 5-10 μm and an aspect ratio of 5)

Fibrous substance C: asbestos fibers (6 Class)

Fibrous substance D: large-size potassium hexatitanate fibers (having asection diameter of 20-50 μm and a length of 100-300 μm)

Fibrous substance E: minute needle-like potassium octatitanate fibers(having a section diameter of 0.2-0.5 μm and a length of 5-15 μm)

COMPARATIVE EXAMPLE 2

The procedure of Example 2 was followed, except that KTMO-a was used inthe place of KTMO obtained in Example 1, to fabricate a disc pad F.

TEST EXAMPLE 1

Frictional Wear Test

For the disc pads obtained in Example 2 and Comparative Examples 1 and2, a constant-rate frictional wear test (friction disc surface: made ofFC 25 gray cast iron, surface pressure: 0.98 MPa, friction speed: 7m/sec) was conducted according to the standards described in JIS D 4411“Automobile Friction Lining” to measure a wear rate (cm3/kgm) and afriction coefficient (μ). The results are given in FIGS. 5 and 6.

Disc Pads A (Friction Material of the Present Invention) and F

Evidently, they exhibit the superior wear resistance over a low to hightemperature range to the disc pad C (containing asbestos fibers) andalso show coefficients of friction relatively stabilized against atemperature change.

Disc Pad D (Containing Large-Size Potassium Hexatitanate Fibers)

Although showing stable wear properties comparable to the frictionmaterial of the present invention, it exhibits the inferior thermalstability as to friction coefficient compared to the friction materialof the present invention.

Disc Pad E (Containing Minute Needle-Like Potassium Titanate Fibers)

Although it has a high friction coefficient and is little affected bytemperature to thereby show a superior stability, its wear amountincreases with a rise of temperature.

TEST EXAMPLE 2

Frictional Wear Test

For the disc pads A and F, a constant-rate frictional wear test wasperformed for 100 hours in the same manner as in Test Example 1 tomeasure a wear rate (cm3/kgm) at each temperature range. The measurementresults are given in FIG. 7.

As can be appreciated from FIG. 7, the disc pad A shows the reducedwearability at a high temperature range, i.e., the superior wearresistance.

EXAMPLE 3

Synthesis of KTMO of the present invention:

KTMO-a obtained in (1) of Example 1 was used to prepare 80 liters of a2% aqueous slurry to which 126 g of a 76% aqueous solution of sulfuricacid was subsequently added. The slurry was stirred for 2 hours and thenadjusted to a pH of 8.5. This aqueous slurry was subjected to treatmentby a centrifugal separator. The resulting cake (solids) was dispensed,dried at 110° C. for 5 hours and then calcined at 600° C. for 12 hoursin an electric furnace. The calcined product was cooled gradually andthen passed through a 20 mesh screen to obtain a white powder with anarithmetic mean of major and minor diameters of 3 μm, a mean thicknessof 300 nm and a proportion of a major to minor diameter of 1.5. Thewhite powder was identified as having a composition ofK_(0.7)Mg_(0.4)Ti_(1.6)O_(3.95) by fluorescent X-ray analysis using anFP method. Also, its melting point was found to be about 1,372° C.

EXAMPLE 4

Synthesis of KTMO of the present invention:

KTMO-a obtained in (1) of Example 1 was used to prepare 80 liters of a2% aqueous slurry to which 189 g of a 76% aqueous solution of sulfuricacid was subsequently added. The slurry was stirred for 2 hours and thenadjusted to a pH of 8.0. This aqueous slurry was subjected to treatmentby a centrifugal separator. The resulting cake (solids) was dispensed,dried at 110° C. for 5 hours and then calcined at 600° C. for 12 hoursin an electric furnace. The calcined product was cooled gradually andthen passed through a 20 mesh screen to obtain a white powder with anarithmetic mean of major and minor diameters of 3 m, a mean thickness of300 nm and a proportion of a major to minor diameter of 1.5. The whitepowder was identified as having a composition ofK_(0.6)Mg_(0.4)Ti_(1.6)O_(3.9) by fluorescent X-ray analysis using an FPmethod.

FIG. 10 is a thermal analysis chart of the obtained white powder. As canbe seen from FIG. 10, its melting point was about 1,375° C.

UTILITY IN INDUSTRY

The present invention provides novel lepidocrocite potassium magnesiumtitanate suitable for use as a friction control agent.

The friction material of the present invention contains the abovelepidocrocite potassium magnesium titanate as a friction control agentand can be suitably used for braking members, e.g., clutch facings andbrake linings incorporated in braking devices as of automobiles,aircrafts, railway vehicles and industrial apparatuses.

1. A lepidocrocite potassium magnesium titanate having a compositionrepresented by the formula K_(0.2-0.5)Mg_(0.4)Ti_(1.6)O_(3.7-4).
 2. Thelepidocrocite potassium magnesium titanate as recited in claim 1,comprising an arithmetic mean of major and minor diameters of 0.1-100μm, a proportion of a major to minor diameter of from 1 to below 5, amean thickness of 50-5,000 nm and a flaky shape.
 3. A method formanufacturing the lepidocrocite potassium magnesium titanate as recitedin claim 1, comprising the steps of: adding an acid to an aqueous slurryof lepidocrocite potassium magnesium titanate having a compositionrepresented by the formula K_(0.8)Mg_(0.4)Ti_(1.6)O₄ so that the slurryis adjusted to a pH of 6-9; separating solids from the slurry; andcalcining the solids.
 4. A method for manufacturing the lepidocrocitepotassium magnesium titanate as recited in claim 2, comprising the stepsof: adding an acid to an aqueous slurry of lepidocrocite potassiummagnesium titanate having a composition represented by the formulaK_(0.8)Mg_(0.4)Ti_(1.6)O₄ so that the slurry is adjusted to a pH of 6-9;separating solids from the slurry; and calcining the solids.
 5. Afriction control agent comprising the lepidocrocite potassium magnesiumtitanate of claim
 1. 6. A friction control agent comprising thelepidocrocite potassium magnesium titanate of claim
 2. 7. A frictionmaterial comprising 1-80% by weight of the lepidocrocite potassiummagnesium titanate of claim
 1. 8. A friction material comprising 1-80%by weight of the lepidocrocite potassium magnesium titanate of claim 2.9. A friction control agent comprising lepidocrocite potassium magnesiumtitanate having a composition represented by the formulaK_(O.2-0.7)Mg_(0.4)Ti_(1.6)O_(3.7-4).
 10. A friction material comprising1-80% by weight of lepidocrocite potassium magnesium titanate having acomposition represented by the formulaK_(0.2-0.7)Mg_(0.4)Ti_(1.6)O_(3.7-4).
 11. The friction material of claim10, further comprising 5-60% by weight of a binder and 1-60% by weightof a fibrous substance.
 12. A method for manufacturing a lepidocrocitepotassium magnesium titanate having a composition represented by theformula K_(0.2-0.7)Mg_(0.4)Ti_(1.6)O_(3.7-4) comprising the steps of:adding an acid to an aqueous slurry of lepidocrocite potassium magnesiumtitanate having a composition represented by the formulaK_(0.8)Mg_(0.4)Ti_(1.6)O₄ so that the slurry is adjusted to a pH of 6-9;separating solids from the slurry; and calcining the solids.
 13. Themethod for manufacturing the lepidocrocite potassium magnesium titanateas recited in claim 12, characterized in that the slurry is adjusted toa pH of 6.5-8.5.
 14. A friction control agent comprising thelepidocrocite potassium magnesium titanate manufactured by the method ofclaim
 12. 15. A friction control agent comprising the lepidocrocitepotassium magnesium titanate manufactured by the method of claim
 13. 16.A friction material comprising 1-80% by weight of the lepidocrocitepotassium magnesium titanate manufactured by the method of claim
 12. 17.A friction material comprising 1-80% by weight of the lepidocrocitepotassium magnesium titanate manufactured by the method of claim 13.